In 10 years the number of patients initiating chronic hemodialysis (HD) annually will double (to approximately 200K). Despite several advances, HD mortality rates remain extremely high. The United States Renal Data System (USRDS) is the largest epidemiological database of US HD patients and serves as the benchmark to guide care. The USRDS and other related databases (e.g., from large dialysis providers), however, lack concomitant blood samples. Therefore, large-scale testing of hypotheses necessitating biological measures potentially linked with adverse outcomes has not been performed, and practice patterns vary greatly. In the spirit of PA- 02-077 - 'rapid analyses of new or existing databases that are innovative and high risk with the likelihood for high impact' - we have initiated a 'USRDS-like' study in collaboration with the largest US dialysis provider to prospectively collect demographic data and biological samples from incident HD patients living throughout the US to test the following aims: 1) HD patients are profoundly vitamin D deficient, yet over half of incident HD patients are not treated with inject able vitamin D. Hypothesis: Higher vitamin D levels (serum 25-OH-D) at HD initiation are associated with lower risk of 90-day and 1-year mortality among patients who do not receive vitamin D therapy; 2) In the diabetic non-HD population, elevated HbAlc levels identify those at increased risk for mortality. Data in the HD population are limited. Hypothesis: Increased HbAlc levels at the initiation of HD are associated with increased 90-day mortality, however, levels taken thereafter (e.g., at 3 months) are not associated with subsequent 1 year survival because HbAlc levels are rendered useless in the setting of erythropoietin therapy and shortened red-cell survival, and both are universal in the HD population. We have already enrolled -2400 incident HD patients with concomitant biological samples, and these patients are representative of the larger USRDS population; projected enrollment is -15,000 from >1000 HD centers and our power is excellent. We have extensive experience in initiating, maintaining, and analyzing large cost-efficient prospective study with biological samples. We have in place detailed plans for the protection of patient privacy, inclusion of all patients, and data/sample sharing with the larger research community.